The identification of genes necessary for establishing pattern formation during morphogenesis and the study of their regulation are relevant to many aspects of vertebrate biology. Many key processes in morphogenesis, including responses to trophic stimuli, cell-cell interactions, migration, differential proliferation, programmed cell death, etc., are recapitulated in a pathologic manner during oncogenesis. So, an understanding of processes active during morphogenesis and their regulation will ultimately contribute to a better understanding of mechanisms of oncogenesis and metastasis, and may provide insight into cancer prevention and treatment strategies. Chick limb development is an attractive system for studying the molecular basis of pattern formation because critical events at the level of tissue/cellular interactions have been well characterized and are very similar to those in mammals, and this system is readily amenable to biochemical and molecular analysis as well as microsurgical manipulation. The aim of this project is to isolate genes that regulate morphogenesis in the chick embryo limb bud. Two approaches are being developed: 1) the generation of subtracted cDNA libraries enriched for potential regulatory and induced genes; and 2) the identification of related/new members of conserved gene families that have been implicated in developmental regulatory processes in other systems. Two novel members of the homeobox gene family have been identified which show spatially restricted expression domains within the limb bud that suggest roles in regulating pattern formation along the anterior-posterior (A-P) and the proximodistal (P-D) axes of the limb. One of these genes is also expressed in the very early embryo during gastrulation, as well as the limb bud, and may regulate the determination of positional identity along the primary embryonic axis, as well as the limb P-D axis. Studies are underway to elucidate the function of these regulatory genes, using both molecular genetic and biochemical approaches.